This invention relates to a device for providing an indication of whether the surface of a body of water, such as a pond or like, has frozen to a predetermined thickness. For example, such a device is useful to warn skaters whether ice is of sufficient thickness so as to be safe for skating, walking or other activity on a frozen body of water. While it is contemplated that one of the primary uses of the invention will be as a safety warning device, it is to be understood that the invention is useable in any other environments where it is desirable to know whether ice has formed to a predetermined thickness. For example, in some instances it may be desirable to know whether the ice is capable of supporting a load of a heavy piece of machinery, vehicle or the like.
In brief, the invention includes a hollow housing which is supported at the surface of the body of water, for example, by floats. The housing defines a sealable chamber and has a portion which extends downwardly into the water. The downwardly extending portion of the chamber is constructed to be expandable and includes a movable member, such as a piston which is slideably received in a downwardly extending neck portion of the housing. When the device is placed into operation, the chamber is filled with water which will expand as it freezes to cause the movable member to move from its normal position. The housing carries an indicator device which extends upwardly from the housing so as to be visible from a distance. The indicator device is connected to the movable member and they are normally biased in a normal configuration in which the chamber and the movable member are in an unexpanded configuration and in which the indicator is in a "warning" configuration. As the body of water freezes, the water within the expansible chamber will freeze at the same rate and in the same manner so that the thickness of ice in the chamber will correspond to the thickness of ice in the surrounding body of water. As the water within the chamber freezes progressively in a downward direction, the expansion of the freezing water within the chamber urges the movable member downwardly to a position which will cause the indicator to change its signal, thus indicating that the ice is at least of that predetermined thickness.
It is among the general objects of the invention to provide a device which provides a discernable signal that the surface of a body of water has become frozen to a predetermined thickness.
Another object of the invention is to provide an ice thickness indicator of the type described which may be placed permanently in the water.
A further object of the invention is to provide an ice thickness indicator of the type described which is capable of providing a visual indication of the thickness of the ice from a distance.
Another object of the invention is to provide an ice thickness indicator of the type described which is of simple and comparatively inexpensive construction.